Sarcogyne clavus (DC) Kremp.

    Thallus more or less immersed and hardly visible or as a greyish or blackish tinge of the substratum. Apothecia sessile, constricted towards the base and almost stalked, 1-4 mm diam., disc flat to slightly convex, dark red to red-blackish according to hygrometry, not pruinose, exciple persistent sometimes irregular by compression with neighbours, prominent, crenulate, blackish. Asci containing very numerous spores (over 200). Ascospores simple, ellipsoid, 4-5 x 1,5-2 µm. Photobionte : Myrmercia. Chemical spot tests negative. Strong coastal trends, grows in small crevices of siliceous rocks. Not to be confused with Sarcogyne hypophaea, that is not especially maritime, and characterized by apothecia with persistent exciple, not crenulate  though sometimes distorted by neighbours and with Sarcogyne regularis of which the apothecia often are powdery with a thin exciple soon excluded  and grows on calcareous rocks or mortar. On mortar and calcareous rocks, avoid confusion with Clauzadea monticola of which the apothecia are more globose, exciple excluded rapidly and asci 8-spored.*